This invention relates to a thread cutting device for a sewing machine of chain sewing, particularly to one having an extending distance of a movable knife shortened to make sure thread hooking and cutting process, and able to adjust an error of the extending distance of the movable knife if it should occur.
A variety of sewing machines are in use in textile industry, and the sewing machine of chain sewing is widely utilized, with a thread cutting device added on the table of the sewing machine for automatically hooking and cutting threads when sewing operation is finished for enhancing working efficiency.
A conventional thread cutting device for the sewing machine of chain sewing shown in FIGS. 17 and 18 includes a clamping device 10, a swing arm 20, a slide guider 30 and a fixing plate 40.
The clamping device includes a movable knife 101, a main knife 102, an upper lamp 103, and a lower clamp 104 combined together. The main knife 102, the upper and the lower clamp 103 and 104 are fixed on a front end of the fixing plate 40 after combined together, with the movable knife 101 protruding through the clamp device 10 and fixed on a front end of the slide guider 30. The swing arm 20 is fixed at a point in an intermediate portion with the table of the sewing machine to function as a fulcrum, having a long slot 202 in an outer end for a slide pin 301 of the slide guider 3 to fit and move therein. The slide guider 30 is fitted in a limit opening 401 of the fixing plate 40, and the swing arm 20 has its inner end connected with a transmitting unit of the sewing machine so that the swing arm may be swung to force the slide guider moved back and forth. Further, the fixing plate 40 has a hole 402 respectively in four corners for screws to fix the whole cutting device on the table of the sewing machine.
Next, referring to FIG. 18, in operation of the sewing machine, a weaving thread or warp 50 moves up and down with the needle to insert in a surface of a cloth being sewn, forming circles 501, and a woof 601 insertted through the hook maker 60 may protrude in the circles 501 by movement of the hook maker 60, and then both the warp 50 and the woof 601 are pulled by the cloth for a certain length, and forcing them 50 and 60 twist together to form a stitch on the rear side of the cloth, completing sewing operation.
In cutting the threads or the warp 50 and the woof 601 on completion of sewing, the movable knife 101 is extended forward by the swing arm 20, with a front hook 105 of the movable knife 101 inserting through and expanding the warp 50 as shown in FIG. 19. Next, the movable knife 101 continues to extend forward and passes through the circles 501 to reach an outermost point and stop there as shown in FIG. 20. Then the movable knife 101 begins to be retracted back, with the front hook 105 and the rear hook 106 of the movable knife 101 respectively hooking the woof 601 and the warp 50 and retracting them to reach an innermost point as shown in FIG. 21. Then the warp 50 hooked is cut off by the main knife knife 102, and the woof 601 is cut off and clamped between the upper and the lower clamp 103 and 104 as shown in FIG. 22. Thus, thread cutting operation is completed, and the thread cutting device is ready for the next sewing operation.
However, the conventional thread cutting device has been found to have disadvantages as follows.
1. The hook maker 60 moves for a certain angle with the up and down movement of the needle, and if the needle moves up and down 3000 times per minute, the hook maker 60 also moves the same times. And the thread cutting device has to be installed enough far from the hook maker so as to avoid moving scope of the hook maker to protect the cutting device from damaged by collision with the hook maker. Thus, the moving distance of the movable knife 101 has to be lengthened for smoothly hooking and cutting the threads so that its extending-out distance may easily cause malfunction of thread hooking and cutting, with the threads to be anew inserted through the eye of the needle and thus causing troubles to a worker. PA1 2. The thread cutting device is located comparatively far from the hook maker and the needle, the threads protrude out too long after they are cut, retracted by the movable knife, impairing outer appearance of a finished product. PA1 3. The fixing plate is fixed on the table of a sewing machine with screws engaging holes in four corners, so the screws have to be loosened and removed if the whole thread cutting device should be adjusted in location so as to keep cutting process smooth after a period of use. So it needs a troublesome work to adjust its location.
The above conventional thread cutting device for a sewing machine of chain sewing is disclosed in a U.S. patent Ser. No. 548199 by the same inventor of this new application.